error Unexpected C# extractor error: Unhandled literal type

When running CodeQL against a medium size c# repo, single solution, multiple DLL's on .Net, codeQL returns:
error Unexpected C# extractor error: Unhandled literal type

Below is an extract from the CodeQL log showing the error:
============

Intepreted metric query "Total lines of code in the database" (cs/summary/lines-of-code) at path C:\hostedtoolcache\windows\CodeQL\0.0.0-20210921\x64\codeql\qlpacks\codeql-csharp\Metrics\Summaries\LinesOfCode.ql.
486
Analysis produced the following diagnostic data:
487

488
| Severity | Message |
489
+----------+-------------------------------------------------------------+
490
| error | Unexpected C# extractor error: Unhandled literal type |
491
| none | (750 results for diagnostic "Successfully extracted files") |
492
Analysis produced the following metric data:
493

494
| Metric | Value |
495
+-------------------------------------+-------+
496
| Total lines of code in the database | 56198 |
497
Analysis produced the following diagnostic data:
498

499
| Severity | Message |
500
+----------+-------------------------------------------------------------+
501
| error | Unexpected C# extractor error: Unhandled literal type |
502
| none | (750 results for diagnostic "Successfully extracted files") |
503
Analysis produced the following metric data:
504

505
| Metric | Value |
506
+-------------------------------------+-------+
507
| Total lines of code in the database | 56198 |
508

509
C:\hostedtoolcache\windows\CodeQL\0.0.0-20210921\x64\codeql\codeql.exe database print-baseline D:\a\_temp\codeql_databases\csharp
510
Counted a baseline of 139483 lines of code for csharp.
511
Counted a baseline of 139483 lines of code for csharp.